So I just brought a new light to use whilst on the computer, this got me thinking, most posts you see about graphics mention the importance and correct set up of the monitor colours but how much affect does room lighting have on what your actually seeing.

It can affect your result as seen by others for sure. There are a lot of monitor calibration tools that try to compensate for even ambient lighting. I don't use them; I try to use a warm florescent (as opposed to the standard bluish color florescenct lights). I look at other monitors when I can my edits and am still happy with the result. The biggest thing to remember is you are sharing your work with others and each has a hodgepodge of settings and you are to guess at which is the biggest common denominator. I do occasionally go through the manual calibration process that Win7 steps you through and, for the most part, it gives me decent results when I look at my retouches from other folks monitors. The biggest thing to remember is to make sure you edit in sRGB since that's pretty much king in the web domain. It may not be the best color space to work with, but most printers can't even exceed this space (accept the uber high end inkjets) so I'm pleased with my print output too.